4 files changed, 28 insertions, 19 deletions
diff --git a/src/cmd/compile/internal/gc/bitset.go b/src/cmd/compile/internal/gc/bitset.go
index 89e6fe85c8..90babd5a9f 100644
--- a/src/cmd/compile/internal/gc/bitset.go
+++ b/src/cmd/compile/internal/gc/bitset.go
@@ -28,20 +28,22 @@ func (f bitset32) get2(shift uint8) uint8 {
 	return uint8(f>>shift) & 3
 }
 
+// set2 sets two bits in f using the bottom two bits of b.
 func (f *bitset32) set2(shift uint8, b uint8) {
 	// Clear old bits.
 	*(*uint32)(f) &^= 3 << shift
 	// Set new bits.
-	*(*uint32)(f) |= uint32(b) << shift
+	*(*uint32)(f) |= uint32(b&3) << shift
 }
 
 func (f bitset32) get3(shift uint8) uint8 {
 	return uint8(f>>shift) & 7
 }
 
+// set3 sets three bits in f using the bottom three bits of b.
 func (f *bitset32) set3(shift uint8, b uint8) {
 	// Clear old bits.
 	*(*uint32)(f) &^= 7 << shift
 	// Set new bits.
-	*(*uint32)(f) |= uint32(b) << shift
+	*(*uint32)(f) |= uint32(b&7) << shift
 }
diff --git a/src/cmd/compile/internal/gc/gen.go b/src/cmd/compile/internal/gc/gen.go
index fffc5b76dd..941c41502a 100644
--- a/src/cmd/compile/internal/gc/gen.go
+++ b/src/cmd/compile/internal/gc/gen.go
@@ -24,10 +24,11 @@ func Sysfunc(name string) *obj.LSym {
 // to be taken.
 func addrescapes(n *Node) {
 	switch n.Op {
-	// probably a type error already.
-	// dump("addrescapes", n);
 	default:
-		break
+		// Unexpected Op, probably due to a previous type error. Ignore.
+
+	case OIND, ODOTPTR:
+		// Nothing to do.
 
 	case ONAME:
 		if n == nodfp {
@@ -73,9 +74,6 @@ func addrescapes(n *Node) {
 		Curfn = oldfn
 		lineno = ln
 
-	case OIND, ODOTPTR:
-		break
-
 	// ODOTPTR has already been introduced,
 	// so these are the non-pointer ODOT and OINDEX.
 	// In &x[0], if x is a slice, then x does not
diff --git a/src/cmd/compile/internal/gc/go.go b/src/cmd/compile/internal/gc/go.go
index 46cec3e8bc..f795ce0bf0 100644
--- a/src/cmd/compile/internal/gc/go.go
+++ b/src/cmd/compile/internal/gc/go.go
@@ -31,17 +31,25 @@ func isRuntimePkg(p *types.Pkg) bool {
 type Class uint8
 
 const (
-	Pxxx      Class = iota
-	PEXTERN         // global variable
-	PAUTO           // local variables
-	PAUTOHEAP       // local variable or parameter moved to heap
-	PPARAM          // input arguments
-	PPARAMOUT       // output results
-	PFUNC           // global function
+	Pxxx      Class = iota // no class; used during ssa conversion to indicate pseudo-variables
+	PEXTERN                // global variable
+	PAUTO                  // local variables
+	PAUTOHEAP              // local variable or parameter moved to heap
+	PPARAM                 // input arguments
+	PPARAMOUT              // output results
+	PFUNC                  // global function
 
 	PDISCARD // discard during parse of duplicate import
+	// Careful: Class is stored in three bits in Node.flags.
+	// Adding a new Class will overflow that.
 )
 
+func init() {
+	if PDISCARD != 7 {
+		panic("PDISCARD changed; does all Class values still fit in three bits?")
+	}
+}
+
 // note this is the runtime representation
 // of the compilers arrays.
 //
diff --git a/src/cmd/compile/internal/gc/sinit.go b/src/cmd/compile/internal/gc/sinit.go
index e8f3d70bd1..1a1dbc0de7 100644
--- a/src/cmd/compile/internal/gc/sinit.go
+++ b/src/cmd/compile/internal/gc/sinit.go
@@ -9,11 +9,12 @@ import (
 	"fmt"
 )
 
-// static initialization
+// Static initialization ordering state.
+// These values are stored in two bits in Node.flags.
 const (
-	InitNotStarted = 0
-	InitDone       = 1
-	InitPending    = 2
+	InitNotStarted = iota
+	InitDone
+	InitPending
 )
 
 type InitEntry struct {